1. Field
The following description relates to an analog-to-digital conversion technique, and more particularly, to an analog-to-digital conversion technique using a flash method combined with a folding method.
2. Description of the Related Art
Along with increasing demand for broadband digital communication, optical storage apparatuses, and the like, demand for analog-to-digital converters (hereinafter, referred to as “ADCs”) with higher conversion speed and higher resolution is also increasing. The ADC is a device which converts input analog signals into digital signals with one of a voltage form and a current form.
As examples of a high-speed ADC, a flash ADC, a folding and interpolating ADC, a pipeline ADC, and the like may be given.
The flash ADC is a parallel comparison type ADC, and converts analog signals into digital signals. The flash ADC is suitable for applications which require a wide bandwidth and high-speed processing, and does not sequentially calculate only one clock cycle at a time, but simultaneously completes all the analog-to-digital conversion processes.
The flash ADC uses a method of comparing analog input signals with a reference voltage divided by several resistor ladders, using each comparator. In order to obtain an N-bit flash ADC, 2N−1 number of comparators and 2N number of resistors are required. When a comparison voltage is applied to the resistors in a ladder configuration, the comparators at each level of the resistor ladder generate a logical bit in order of decreasing significance as the ladder is descended.
Each comparator returns “1” when the analog input signal is larger than the comparison voltage, and returns “0” when the analog input signal is less than the comparison voltage.